OSOcean ScienceOSOcean Sci.1812-0792Copernicus PublicationsGöttingen, Germany10.5194/os-8-419-2012Influence of Ross Sea Bottom Water changes on the warming and freshening of the Antarctic Bottom Water in the Australian-Antarctic BasinShimadaK.1AokiS.1OhshimaK. I.1RintoulS. R.42351Institute of Low Temperature Science, Hokkaido University, Sapporo, Japan2CSIRO Marine and Atmospheric Research, Hobart, Tasmania, Australia3Centre for Australian Weather and Climate Research, Hobart, Tasmania, Australia4Antarctic Climate and Ecosystems Cooperative Research Centre, University of Tasmania, Hobart, Tasmania, Australia5CSIRO Wealth from Oceans National Research Flagship, Hobart, Tasmania, Australia0907201284419432This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/This article is available from https://www.ocean-sci.net/8/419/2012/os-8-419-2012.htmlThe full text article is available as a PDF file from https://www.ocean-sci.net/8/419/2012/os-8-419-2012.pdf

Changes to the properties of Antarctic Bottom Water in the
Australian-Antarctic Basin (AA-AABW) between the 1990s and 2000s are
documented using data from the WOCE Hydrographic Program (WHP) and repeated
hydrographic surveys. Strong cooling and freshening are observed on isopycnal
layers denser than <i>&gamma;<sup>n</sup></i> = 28.30 kg m<sup>−3</sup>. Changes in the average salinity
and potential temperature below this isopycnal correspond to a basin-wide
warming of 1300 ± 200 GW and freshening of 24 ± 3 Gt year<sup>−1</sup>. Recent
changes to dense shelf water in the source regions in the Ross Sea and
George V Land can explain the freshening of AA-AABW but not its extensive
warming. An alternative mechanism for this warming is a decrease in the
supply of AABW from the Ross Sea (RSBW). Hydrographic profiles between the
western Ross Sea and George V Land (171–158° E) were analyzed with a
simple advective-diffusive model to assess the causes of the observed
changes. The model suggests that the warming of RSBW observed between the
1970s and 2000s can be explained by a 21 ± 23% reduction in RSBW
transport and the enhancement of the vertical diffusion of heat resulting
from a 30 ± 7% weakening of the abyssal stratification. The documented
freshening of Ross Sea dense shelf water leads to a reduction in both
salinity and density stratification. Therefore the direct freshening of RSBW
at its source also produces an indirect warming of the RSBW. A simple box
model suggests that the changes in RSBW properties and volume transport (a
decrease of 6.7% is assumed between the year 1995 and 2005) can explain
51 ± 6% of the warming and 84 ± 10% of the freshening observed in
AA-AABW.